Hi all I am looking for some advice. I am planning to move my iTunes Library and iPhoto Library and all my primary file storage to an external 3TB USB3 drive formatted in exFat so if my Mac fails I can connect it to my Windows server and retrieve my data. I made a test copy of my files to make sure everything worked and I noticed something interesting. When I look at the properties of my new directory on the exFat drive it tells me it is 741 GB but when I look at the properties of the same directory on the old Mac OS Extended Journaled Volume it tells me the size is 634 GB for the exact same amount of files. Any idea why there is a 100GB difference for the same amount of files? Does exFat store the files differently for some reason?

Seems I partially answered my own question. Looks like by default HFS+ used 4k clusters for the file system and my exFat was formatted with 256k clusters. Anyone know if there is a utility to format in exFat with smaller clusters? There does not seem to be a way to do this in the GUI on Mac or Windows. Can exFat use smaller clusters?

Ok so using the format command line utility in windows I was able to format the drive as exFat using 4096 byes per allocation unit or cluster and now the files are the same size on the HFS and the exFat volumes. For some reason the GUI in Windows does not let you choose below 256 kbytes and Mac OS automatically selects 256 kbytes (at least on Lion) and does not even give you the option of choosing. I wonder who makes these programming decisions anyway.

A lower block size means more overhead to store the contents of files. Especially for large files. The primary motivation for exFAT was to get around the 4GB max file size limit in FAT32. So I'm guessing the programmers were assuming the user would be storing larger files on the device instead of lots of small files. Otherwise, the user would use FAT32.

The bad thing about using exFAT is that you are giving up a lot of Mac functionality. You can't use the drive for backups and you won't be able to encrypt the drive. But if you require Windows compatibility, then it's still your best choice.

Thanks for the response. Encryption is not a big deal to me and for backup I plan to use ChronoSync to sync the files to a folder on my Drobo. I will be using this as my primary file storage since my SSD has limited space and my iTunes and iPhoto Libraries are over 60GB each. I am not looking for super advanced file system just something to hold my files and be reliable, and have cross-platform support. I wont use Fat32 because it is just so outdated and I do need to store files over 4GB eg. disk images etc. Are there any other limitations I should be worried about?